1. Field of the Invention
The present invention relates to an optical element and an illumination apparatus having the same. More specifically, the present invention relates to an optical element or an illumination apparatus having an optical element in which a light flux emitted from light source means is shaped so that line illumination would be efficiently effected. The optical element and the illumination apparatus according to the present invention would be preferably used in an image reading apparatus that utilizes a one-dimensional line sensor.
2. Description of the Related Art
Recently, as an apparatus for providing a line illumination for an image reading apparatus, there have been proposed various illumination apparatus that uses a light source (a point source) composed of a semiconductor device and effectively converges a light flux emitted from the light source onto the surface of an original to be illuminated. The light source composed of a semiconductor device is adopted in view of its advantages that its power consumption and heat generation are little and it does not require any particular lighting device.
In this type of illumination apparatus, multiple light sources composed of semiconductor devices are arranged in the direction parallel to the line direction of the one-dimensional line sensor, and light fluxes emitted from the multiple light sources are converged onto the surface of an original by means of a single elongated reflecting member (or an optical element). Such an illumination apparatus was proposed by Japanese Patent Application Laid-Open No. 11-52136.
However, efficient light conversion is highly sensitive to manufacturing error, and therefore, a high accuracy in its shape and its maintenance is required. This causes the following problems.
(1) Since the size of the reflecting member is large, the mold used for manufacturing the same becomes large and its cost is very high.
(2) Since the size of the reflecting member is large, it would deform after detached from the mold due to residual stress applied during the molding.
(3) The relative positional relationship between the light source and the reflecting member is sensitive, and therefore curvature cannot be corrected satisfactorily.
(4) Since the reflecting member is designed in conformity with the size of the original, it lacks versatility.